The present invention is directed to provide an improved device for controlling a DC motor for operation on both directions of rotation.
A device of this type comprises first and second control reversing switches for controlling the motor rotation in a first direction and in a second direction of rotation, respectively, each one of said reversing switches being inserted in one of the two conductors supplying current to the motor. These switches have their common terminals disposed on the side of the two motor terminals, respectively, and their first and second terminals coupled to the positive and negative terminals, respectively, of the current source. This control device further comprises first and second ON-OFF switches adapted to stop the motor when the latter rotates in the first and second directions of rotation, respectively, each ON-OFF switch being connected in series to one of said control reversing switches, respectively, between the corresponding reversing switch and the motor, and two unidirectional starting elements each connected in parallel to one of said ON-OFF switches, the anode and cathode of each unidirectional starting element being located adjacent the motor. In addition, both ON-OFF swtiches consist of reversing switches comprising each a common terminal connected directly to the motor, a first terminal connected to the common terminal of the control reversing switch connected in series to said ON-OFF switch, and a second terminal connected to the common terminal of the other ON-OFF switch of the pair via a unidirectional stopping element. Finally, the cathode, or the anode, of each unidirectional stopping element is connected to the common terminal of the other ON-OFF switch when the anode, or the cathode, of the unidirectional starting element is disposed on the motor side.
Such device is disclosed in the U.S. Pat. No. 2,912,632 and further comprises resistors in series with diodes interconnecting the reversing switches. The possibility of stopping the motor suddenly and instantaneously is not contemplated; only a slow-down action for dissipating the current is provided. Moreover, when the single control reversing switch is actuated, the motor is not braked, and this may constitute a source of serious troubles.